Thank you so much to bologna who started this thread. I was going to go the 06.15.00 route until I saw this post by bologna who put it so succinctly. It became obvious to me that this was not the route I wanted to take. Then thanks to further posts about Fuzzyband. I have a 3G which had an accidental update. I downgraded it to iOS 3.1.2 and did the jailbreak with redsn0w only to find out that my baseband was updated to 05.15.04 and couldn't unlock with ultrasn0w. So then came Fuzzyband. I downloaded and ran it and it said it couldn't do it even though I have boot loader 5.8 which it is suppose to be able to do. A little more research and I was able to install a 05.15.04 certificate file into Fuzzyband which then allowed it to work and thus downgrade my baseband to 05.13.04. I then unlocked with ultrasn0w and am back up and running again. Thanks so much all!

snip -- I downgraded it to iOS 3.1.2 and did the jailbreak with redsn0w -- snip

can you elaborate on how you achieved this downgrade?
which FW ver. did u start off with?
did this downgrade involve having previously stored SHSH blobs?
i'm new to JB/unlocking, so don't have any previous SHSH blobs backed-up.

I have a 3gs jb+unlocked bl 06.04 bb 06.16.00 mc136ll fully working gps works no issues with wifi or battery drainage issue..i just want to know if i cant continue to just keep updating to ipad future basebands ha i mean why not if im already f#cked on it for switching i mean when i restored i knew apple would flash my baseband to the most recent 3gs bb that had no carrier unlock. I didnt have any shsh on file so i was just playing it by whatever, anyways from now on i suppose ill have to update custom firmwares but i mean my iphone works flawless and im pretty stoked.

(to anyone who might use this)
this is how it occurred

I restored to 4.3.3 regularly through ituness 10.2.2 used redsn0w rc15 with 4.3.2 ispw (flashed to ipad fm during process) After the pineapple man finished and my baseband was flashed my phone froze up at the apple screen and would only load up to that screen after some random googling i ran redsn0w rc16 with the bug fix with 4.3.3 ispw flashed it again(dont know if that makes a difference) this time it loaded up to the itunes activation screen i was kinda suprised anyways ran the sn0w rc15 with 4.3.2 again this time not flashing, jb worked used ultrasn0w 1.2.3 to unlock..phones been working..but anyways heres my question again can i keep riding it out with the 06.15.00 since there is noway to downgrade with 06.04 currently and continue using custom firmwares for future updates

p.s im a mac

oh **** i forgot i used tiny umbrella to kick the apple loop anytime i got it

can you elaborate on how you achieved this downgrade?
which FW ver. did u start off with?
did this downgrade involve having previously stored SHSH blobs?
i'm new to JB/unlocking, so don't have any previous SHSH blobs backed-up.

thanks in advance

I started with firmware 4.x something. I had an iTunes update (by accident which gave me the latest and erased the previous jb/unlock that was done).

1. Make sure hosts file in clean, then use iTunes to update the iphone to latest
2. Download 3.1.2 firmware and downgrade (3.1.2 is best for iphone 3g)
-put into recovery mode
-shift click iTunes to restore from 3.1.2 firmware
-let it proceed finalizing with 1015 error
-don't disconnect phone, close iTunes, open iRecovery (iRecovery needs libusb-win32)
- C : \ irecovery.exe -s
- setenv auto-boot true
- saveenv
- fsboot
- fsboot (still didn't reboot, so I manually pressed the power button)
3. Now that 3.1.2 is installed and everything is normal, run redsn0w to jailbreak
-use redsn0w 0.9.2 (won't work with any other version)
4. Setup networking so that you can start cydia
-because of this old version of redsn0w, this cydia is old
-cydia will take a while to startup, then it will ask to update
-the update will take a while and then you'll need to restart cydia
5. I had baseband 05.15.04, there was no unlock for this baseband as of May 3,2011.
I was able to use Fuzzyband to downgrade the baseband to 5.13.04 because I have an older bootloader version
- Fuzzyband from Cydia
- afc2add from Cydia so that iFunBox will work
- iFunBox.exe on windows
- ICE2-05.15.04.cer on windows
- Connect your iPhone to the computer.
- Launch i-FunBox and select File, then go to Applications/Fuzzyband.app.
- Right-click and then select Copy from PC.
- Copy ICE2-05.15.04.cert you have downloaded earlier to this location.
- Go back to Fuzzyband and you can now begin the downgrade process.
If the downgrade is successful, you should see “I Haz Downgrade“. You can now unlock it with ultrasn0w.
6. Ultrasn0w to unlock
-"Search"->utlrasn0w->click
-After ultrasn0w loaded I clicked reboot springboard
-This crashed the shutdown and was frozen on the spinning wheel. I had to hold power/home together to force a hard shutdown
-I inserted the SIM and turned it on. After about 60 seconds, it found t-mobile.